Through a study of the horizontal spread of earth gases in controlled digging, it is known that the length of the spreading zone into the dug trench axis depends upon the porosity and dampness of the soil or other earth strata. Furthermore, it is known from DE-OS No. 2705584 that the surface directed expansion of gas under pressure depend upon the thickness and dampness of the soil. This knowledge is also used for the methods of determining the thickness of underground oil deposits.
It is a problem of the following invention to provide methods and equipment based upon the diffusion of gas through the earth and stone, which can make it possible to investigate the structure and porosity in earth and stony regions for the purpose of protecting natural or constructed dams from percolation and reduction of strength, controlling and preventing washouts due to local strata formations, locating underground cavities, to recognize tectonic stratification, other underground deposits and stratification embankments, all in a reliable and harmless way.